The present invention relates to a dustproof transparent member fitted to a window of a container for containing an optical system or the like.
Laser printers are increasingly being used for obtaining hard copies of image data on recording paper and particularly small-sized, inexpensive printers utilizing semiconductor lasers have increasingly been put to practical use. The laser printer is designed to obtain such hard copies by first exposing a photoconductive drum charged with electricity to a laser beam modulated according to image data such as diagrams and characters, scanning the surface of the photoconductive drum to form an electrostatic latent image, and then subjecting the latent image to a copying process (i.e. the copying process of the so-called electrophotographic system) comprising the steps of developing (i.e. converting the latent image into a toner image), transferring and fixing the image.
In such an image processing apparatus utilizing electrophotographic system as the laser printer, an optical system is normally contained in an independent container in the form of a unit and luminous flux of, e.g. a laser beam 1 is emitted through a window fitted to the container. The window of the container is covered with a dustproof transparent member such as transparent glass, so that toner and other kinds of dust floating in the apparatus are prevented from penetrating into the optical system and sticking to optical parts.
However, because a charger or transfer charger is corona-discharged at high voltages in the image processing apparatus utilizing electrophotography, the dustproof transparent member of the aforementioned container may be charged and consequently the dustproof transparent member may also electrostatically adsorb the dust such as toner floating therein. The problem is that the dust causes the scattering of the luminous flux and a decrease in its transmittance.
Moreover, the toner itself floating in the apparatus often becomes charged and therefore tends to stick to the various parts. As a result, the charged toner may inconveniently stick to the dustproof transparent member of the container even when the dustproof transparent member is not charged.